Synchronizing pulse gating system



VlDro Aug. 30, 1949. w, D. HOUGHTON 2,480,582

SYNCHRONIZING PULSE GATING SYSTEM Filed oct. 18, 1945 2 sheets-sheet 1GATD B PULSE SYNC S Ag @swf R7- Cl ls/Nc PULSE :simu-mpg GATE GEERAWRPULSE g R P R5 R6 28' 9 lo Scmpul E l (sync Purse swam-rang @A1-E@msnm-0R13 @g5 A t1curn'uv` +B f v -3 GTED RL 1 2g 26 I @Las min l yvlnso Puig? n l s `l V7 INPUT l l y l j li- 0 6 I L T sync Puuse -E lag'4 sEPARAToR GATE NERMW INVENTOR.

` g Um/AMD Haz/@MON BY rg/WM irme/wy ug- 30 1949. w. D. HOUGHTON2,480,582

SYNCHRONIZING PULSE GATING SYSTEM Filed Oct. 18, 1945 2 Sheets-Sheet 2T: M E

cHANNEL PuLsss Two sYNC PULSES CHANNEL PULES PULSE mrur Y /2 f-f" ToGATED AMR g 10 l+.

2P' l l) l MT5 F/ ji@ 2a,

MODULATI 0N E AMPL.

- IN VEN TOR. (f/z MM .Z2 wwf/raw me/Vix Patented ug. 30, 1,949

12,480,582.. srNonnoNIziNG PULSE Gli'riNG SYSTEM i.

` signor to RadioCorpo poration ofnDela'ware -Application October 18,1945,@Serial No. 623,127

. This invention relates ratusfor gating orselecting.periodicallyrecurring synchronizing pulses and-*rejecting` all .other.pulses present during the interval between said synchronizingv pulses.l 1 l In pulse receivingr systems it is known tofcon'- trol the timeduring which va desiredvsignal pulse is permitted. to pass through-avacuum tube. This voperationl is usually'achieved by biasing-a tube tocut-off a vcondition during which no anode current flows) exceptforcertaintime intervals during which the signal pulse is expectedtoarrive.A The tube may normally be cut-ofi and conditioned-to lpass thedesired sig-nal pulsebysupplyingto its. control electrode a pulse' ofsu'icient magnitude and polaritytc overcome the cut-oir bias, or in thealternative, 'thetube may normally be conductive and biased-'to cut-offduring those intervals when signalsV arenot to be passed. Stated inlother words, the lvacuumtuloe vfunctions in a manner which is analogousto aigate orfshutter? and is keyed or gatedwat a desired rate'. One'suchmethod of gatingma receiving system, -given -by way "of exampld'isdescribed in'U. S. Patent 2,361,437 granted'October 31,-'1944 to B.Trevor.` l Another method is described in copending U.S.application-SerfNo. 517,814 filed-'January 8,' 1944 by H. O.'Peterson,

now U. S. Patent No. 2,463,094, granted March The present invention is.designedfor use in those systems which utilize'trains of recurringpulses separated-by periodically recurring -controlling orsynchronizingpulses. -The invention nds particular appl-ication'at thereceivingend of a time division multiplex `communication system. s j

-In a vtime division multiplex system, itis customary. to generate' at-the transmitting endv of the system-short pulses of radio frequencyenergy and to transmit these pulses at constant" amplitude and atla xedaverage repetition rate. 1 The pulses in the different-channels aretransmitted consecutively.` These pulses mayfhave their occurrence timeor phase y'modulated within pretermined limits. Thus, a pulse occursfrom each channel once for eachcycle of operation -or synchronizingperiod, and this pulse is advancedfor retarded from itsnormal timevof`occurrence by an amount proportional -to :the `instantaneous amplitudevof the modulation.w During veach cycle of operation or synchronizingperiod,.there are transmitted pulsesirom all ofthe channels followedby asingle. synchronizing pulse of longer duration thanthe channel pulses orbyvtwo or f feciaimfsl (Grits-15) to amel-,hedor and'appa- .more short4synchronizing pulses more closely spaced in time than the consecutivelyoccurring .channel pulses. Asfanfillustration, let it be assumed-thatthere are eight channels; Thenduring each. cycle .of operation Aorsynchronizingiperind, Athere will occurei-ght constant .amplitudepulses. (one for eachchannel) followed by one'or more synchronizingpulses This cycle of `operation repeats -itself continuously'. at. thesynchronizing period.` i l At. thereceivinglendfoi .the multiplexsystem,

it is necessaryto .provide a` circuit for distinguishing `between thechannel pulses and thesynchronizing pulses. The present invention is apulse selective system which achieves this purpose and enables theutilization f of synchronizing pulses.

One of the objects of the present -inventionis to provide a gatingsystem for the synchronizing pulses in order to :prevent interference ormissynchronizing'ldue to noise, ignition radiation,

Briefly stated, the present invention providesat the `receiving Vend ofa vpulse -communicationfsystem,A a pulse-selective system whichdistinguishes between synchronizing pulses and channel pulses, and whichis open -orfv receptive .to the synchronizingpulses for only ashort-period 'of time compared to the synchronizing period. This open orreceptiveinterval occurs at* about the time the synchronizing pulse isdue to arrive at the receiver station.1"*Because the pulse selectivesystem of the invention is"-c1`osed" or-non-receptive in the intervalsbetweenfopen intervals, noise pulsesare prevented from interferingwithfthe synchronizing circuit, and vhence, the signal-tonoiseratio isincreased ycompared to' other sysvtems wherethe synchronizingpulseselector is open for 'the lentire synchronizing` period. v

more detailed description of the invention follows in conjunctionwith adrawing, whereinv 1 Figs. 1,3 and- 4- illustratethreedifferentcircuitembodiments ofthe present invention;r A'and Figs.*2a.to 2ev aregraphical Yrepresentz'altio'ns of voltage waveforms Y.in-'differentparts of the'system,=fgiven to aid in an understanding oftheoperation-oftheinvention. Y j

Throughoutv theflgures ofthe drawing, the same parts 'are representedbythe same reference characters/f v' 'K Referring. to Fig. 1, thereisrshownv onecircuit embodiment of `a pulse` selective'and gating systemof theinventionpcomprisinga gated pulse vacuum tube amplifier I0(pentode or mixer type) to whosefcontrol'electrode the channel andysynchronizingr pulsesare applied; a synchronizing 3 pulse separator il,and a gate generator I3.

The pulses supplied to input terminal 9, which is connected to thecontrol electrode of amplifier tube Iii are video pulses of positivepolarity and of fixed peak amplitude. It should be understood that thesevideo pulses are unidirectional in character 'and constitute the outputof a superheterodyne or other type radio receiver, not shown.

The amplifier I comprises a pentocle but may be a mixer type tube suchas an RCA 6L7. Amplifier I is gated or keyed by pulses applied to itssecond grid over lead 8 from the output of gate generator I3. Ifdesired, amplifier tube III may be a pentode vacuurn tube with. thescreen grid connected as shown in Fig. 3.

The synchronizing pulse; separator I IA comprises a dual diode V2 havingtwo diode sections a and b, a normally conductive triodevacuum tube V3forming part oi a sawtooth generator, and, a normally non-conductive(cut-off) triode vacuum tube V4. y

The gate generator I3 comprises an electronic trigger. C ircuit in theforrn onfY two regeneratively conncctedvacuum tube triodes V5 and Vshaving a, common cathode bias resistor R11. Tube V5 is normallyConductingv and tube Vs, is normally non-conductingin thestable state.The application. Qf; a. negative. pulse to. the. grid; of tube. V5

trips or triggers the circuit into its active state in whichv thecurrent passing conditions of the two tubesl'are reversed. The timeduring which the trigger circuit remains its active state is determinedby the time constants of condenser Cjand resistor Re.4 The triggercircuit restores itself fto the stablestate after the charge oncondenser; @has leaked Olii Output fronl the trigger circuit in the formof a.r pulse. o i negative polarity; is taken via couplingcondenser Caand fed to amplifier i8 over 1.1

lead 8 in order to bias the amplifier to the anode current cut-.offvcondition.

y Theanodes of theditferent tubes in amplier Impulse separator Il andgate generator I3-are Vindividually supplied with anode polarizingpoftentialsover separatev resistors R2, R5, Re, R9 and R19,respectively, lfrom 'the positive terminal -i-B Qfa'source ofunidirectional potential. Y

Ini the" operationof Fig, fl, the normal bias on tube V1 oigthe'pulseamplifier IB Vis set by the values of Ri and C2v in the cathode circuit.In theab'sence offa negative pulse on the second {(#l of tube. V1supplied byv thegate generator I3, anodefcurrent will now in thisamplifierl whenfthernagnitude of thepositive video pulse'sexce'eds thecathode bias developed by R1 and=Cz. These video pulses are of fixedpeak amplitude exceeding this cathode bias. In practice, tube V1 isbiased to a negative value by elements-R1 and C2 so that it conducts atabout half amplitude on the incoming pulses. In the normaloperation ofthis amplifier, the voltage onfthe second grid is reduced during thesynchronizing periodby the negative pulse on lead 8,.supipliled fromgenerator I3, to avalue which prevents anode currentirom flowing in tubeV1. By selecting suitable values `fo'r-thecircuit constantsof the`electronic ftrigger circuit of generator I3, this negative pulse on lead8 terminates inmediately beforethe arrivalof a video synchronizing pulseon input terminal 9. The termination of the negative pulse onlead 8causes thevoltag'e on the second Ygrid of tube-V1 to be raised to zero(value-which permitsanodecurrent-to owjn amplifier. IB when an inputpulse 4 is present on the control grid of tube V1. After the amplier lilhas passed the synchronizing pulse or pulses, the voltage on the secondgrid of tube V1 is again reduced by a negative pulse on lead 3 to thesame low value which prevents anode current from flowing in tube V1.

The invention will first be described in connection with a pulse typemultiplex system utilizingtwo closely' spaced synchronizing pulses whichrecur periodically. Pulses from such a multiplex system are representedin Fig. 2a which shows a series of channel pulses followed by two'synchronizing pulses for each cycle of operation or synchronizingperiod. These synchronizing pulses are more closely spaced in time thanany two adjacent channel pulses in extremes of modulation. In iirststarting up the system of Fig. 1, let us assume the absence of anegative pulse on lead 8 for the full synchronizing period since nosynchronizing pulse has previously arrived to trip) gate generator I3.Before the synchronizing pulseA is applied, to input terminal 3,v tubeV1 will pass. anode current each time a channel pulse is applied toitscontrol grid. The flow of anode current in V1 causes a negative pulse ofvoltage to be developed across anode resistor R2 each time a channelpulse isapplied to V1 and this negative pulse is appliedY to;V dual.diode V2 through coupling condenser C1. The leading (falling) edge ofeach negative pulse causes the cathode of diode section b of dual diodeV2 to become negative as a result of which current flows in diodesection b and produces a negative charge on condenser C3. On thetrailing (rising) edge oi each negative pulse of voltage developedacross R2, current will flow through section a of dual diode Vzintocondenser C1, thus restoring the` charge on condenser C1 to its normalvalue.

The negative voltages developed across condenser C3. are shown in Fig.2b. Condenser Ca isshunted by a resistor R4, and the values of these twoelements are such that the negative charge on C3 leaks. oi to a lowvalue between channel pulses, as shown in Fig. 2b. However, when` two.closely spaced synchronizing pulses occur, there are developed twocorrespondingly closely spaced negative voltages across resistor R2Awhich produce cuniulatively added negative charges on condenser Ca.Stated in other Words, the negative charge on condenser C3 due to therst. synchronizing pulse does not have an opportunity to leak off to alow enough value to cause anode current flow in tube V3 before there isaddedanother negative charge on condenser Cacaused by the closely spacedsecond synchronizirigv p ulser This is shown in Fig. 2b at position A.

'I'.riode V3 is normally conductive. The anode current cut-off value oftubeVs is shown by the n horizontal dash vline in Fig. 2b. It should beobserved that tube rV3 is cut-oli each time a negative charge is builtupon condenser C3, but that the duration-of cut-on` of. tube V3 is overa longer period of time when the two synchronizing pulses are presentthan when the channel'pulses are present. Tube V3A and condenser C4 inits anode circuitlconstitute a; sawtooth waveform generator. When V3 is;cutoff, a.,positive charge builds up linearly onycondenser C4 throughresistor R5, resulting-in a Vvoltage as shown inFig, 2c. The smallfpulses; in Fig. 2c represent the voltage charges 4.builtup oncondenserCi dueto 'the presenceiofchannel 'fpulses Thelarger 'voltagepulse in-.Fig. 2c represents. the voltage charge built up on condenserCfidue tothe. presence. of fthe V'two closely spaced synchronizingpulses which causes ftube Vs to be cutv off for a longer period oftime.Upon the dissipation of the negative` charge on .condenser C3, tube Vsagain conducts and provides a low impedance path to ground for thecoupling condenser C5 and is used to trip the electronic trigger.circuit V5, Vs of the gategenerator I3. from its stable to its activestate. As mentioned before, tube V5 is normally conducting and ytube Enormally non-conducting. Tube Vais normally non-conducting due tothevoltage developed across the common cathode resistor R11 by the currentflowing therein. Current'normally flows in tube V5 because its grid isconnected to +B through resistor R3. The application of va negativepulse, Fig. 2d, to the grid of V5 causes tube Vsfto out off and allowstube Vs to conduct. When tube kVe' starts torconduct, therev is produceda negative voltageacross resistor R which further biases tube V5 below'c ut off, by virtue of the regenerative coupling condenserV Cv. Thetrigger circuitY remains inthe active state until' the charge oncondenser C7 leaks off through resist/or Rs. Af 'lube'Varemains kcutoff, therefore, for a time interval determined by the time constants ofcondenser C7 and resistor Rav` The values of condenserC'z and resistorRe 'are' so chosen that the trigger circuit restores itself to thenormal stable state after a time slightly less than the synchronizingperiod.

'As a result of this operation, a negative pulse A is developed `acrossresistor R10 having aduration slightly shorter than the synchronizingperiod. This negative pulse is coupled via condenser Cs and lead' tothesecond or number 2 grid of tube VVV1 of the amplifier lil and keys orgates amplifier I0 so that tube V1 is cut off during the major part ofthe synchronizing period or for thedurajtion of thenegative pulse onlead 8. Hence, am'- plifier IB isV cut-off duringl that portion of thesynchronizing period when the channel pulses are present. Any noise' orignition interference which might be present on input terminal '9 duringthe time V1 is cut off can have no elect on the amplifier [D of thepulse selective system of the invention yand cannot causemis-synchronization. Obviously, mis-synchronization due to noise' jisthus conined to the interval when amplier vIl) vis open or responsive,which occurs just preceding the arrival of the synchronizing pulses.Since noise israndom incharacter and doesl not recur at the same rateand timeas the synchronizing pulses it Will be evident 'that the presentinvention results in an increase in the signal-tonoise ratio inmultiplex systems using pulse type synchronization. v i c Output pulsesfrom the system of the invention are taken from terminal I4 which isconnected to the anode of tube V4. These output pulses are of negativevoltage as shown in Fig. 2d, and are repeated once for each`synchronizing period. and can be utilized tol synchronize or controlthe re;- Aceiving channelselectors, not shown.

Fig. 2e represents the Wave form appearing at -the anode of tube V5'.

This is a negative pulse csinceVs isfcut-off and its anode potential isthere fore equal to +B up to a time just prior to the arrival of thesynchronizing. pulse, at which time the gate generator circuit returnsto its normal or'fstable condition. The arriving synchronizing .pulsecauses tube V5 to again cut-off and thus drive the flip-flop circuittoits unstable condi- ,.tion. It remains in this state for aperiod of time'slightly shorter than the synchronizing period. 10

, torily in pulse multiplex systems wherein only a single synchronizingpulse of longerr duration than the channel operation.

The system of Fig. 1 can also be used satisfacpulses is used foreachcycle rof Fig. s'shcws a modincauoncf the'system of i Fig. l, for 'useat the receiving end of a pulse multiplex system using a singlesynchronizing pulse Lwhich is of longerv duration than the channelpulses.v 'This longer duration l synchronizing pulse takes the place ofthe two closely spaced 1 v synchronizing pulsesv of Fig. 2a,`and occursonce Fig. 3, the negative pulses developed across -sistor R2 are coupledto the grid ofnormally con- -ducting tube V3 via condenser C1.

for` each cycle of operationv or synchronizing The'systemiof Fig. 3 issimilar to that of Fig., 1

Fig. 1 iseliminatedin Fig. 3 and ,the amplifier tube I0" is va pentodevacuum tube .connected somewhatdifferentlyfrom that of'v Fig. .1., In

Eachnegativepulse carries tube'Vs to cut 01T, and as a result causescondenser C4 to chargeup through Vresistor R5.

fC4 form a sawtooth waveform generator. Con- As in Figi, tube V3 andcondenser denser C4 chargesup to a higher value when the ylongerdurationsynchronizing pulse is present because tube V3 is then cut oi for alonger period wjof time than in the presence of channel pulses.

The rest Aof the system of Fig. 3 operates -in'the vsame manner as Fig.1.

' Fig-4 illustrates another-embodiment of the inventionin which onlytriode tubes are employed.

This embodiment is also designed for use in" such pulse multiplexsystems which use a single synfchronizing pulse -of longer duration thanthe channel pulses, although by the'addition of a diode as in Fig. 1,this embodiment canbe used for either system. Fig. 4 includes anadditional-tube V7 which is normally" biased 'to' the anode currentcut-off condition and controlled by a positive output pulse from thetrigger circuit V5. Vs via coupling condenser C9' and lead 1. The grid"of tube 1 is supplied with a negative' bias via resistorRnandthenegative terminal of a uni- 'directional source of potential-E. rlhisnegative bias'is of such magnitude as to prevent 'the flow of currentthrough the tube.

The'gate generator I3 supplies a positive pulse to the' gridof tube Vvof such magnitude as to overcome the negatii/'e bias on tube Vr; andcause this tube to conduct. j When tube V7 conducts, it develops apositive voltage across resistor Riaan'd vthis positive voltage issupplied via ylead 6 to the cathode of tube V1', and biases tube V1'below cut-off for the duration of this positive pulse regardless ofthemaximum peak amplitude of.v the video pulses lsuppliedfto thev grid ofVi. lhe video pulses are passed throughlimiters before being'applied tothe grid of tube V1', hence all pulses are constantamplitude. Theduration of this positive pulse` (applied tothe cathodeof tube Vi) isfor the major part of the synchronizing period, as in the case of Figs.1 and 3.v The remaining portions of Fig. 4 operate in the same manner ascorresponding portions of Fig. 1.

What is claimed is: l

l. In a time division pulse multiplex communication system wherein aplurality of intelligence carrying channel pulses and one or moresynchronizing pulses are transmitted during each synchronizing period, areceiving station having apparatus thereat for producing from saidreceived synchronizing pulses other pulses which occur once eachsynchronizing period, said appa- Vra'tus including an amplifiermulti-electrode tube Vmagnitude and polarity as to prevent the flow orcurrent in said amplifier for the major portion of the succeedingsynchronizing period.

Y 2. In a time division pulse multiplex communi- .cation system whereina plurality oi intelligence carrying channel pulses and one or more syndchronizing pulses are transmitted each synchronizing period, a receivingstation having apparatus thereat for producing from said receivedsynchronizing pulses other pulses which occur onceeach synchronizingperiod, said apparatus including a multi-electrode amplifier tube andmeans for supplying to said amplifier tube pulses -representative of thereceivedintelligence carrying channel pulses and the synchronizingpulses, a circuit coupled to the output of said amplifier for producingvoltages of one amplitude in response to the channelpulses and voltagesof a higher amplitude in response to the synchronizing pulses, anelectron discharge tube coupled to the 'output of said last circuit andnormally biased to be non-conductive, said tube being responsive only tovoltages of said higher amplitude in order to pass current, anelectronic trigger circuit coupled to. and responsive to the ow ofcurrent in vsaid electron discharge tube ior producing a pulse, and afeed-back circuit from said trigger circuit to an electrodeof saidamplier, the pulse produced by saidA trigger circuit having suchduration, magnitude and polarity as to prevent the `flow of current insaid amplifier for the major portion of the succeeding synchronizingperiod.

3. In a time division pulse multiplex communication system wherein aplurality of` intelligence carrying channel pulses and cneor moresynchronizing pulses are transmitted each synchronizing period, areceivi'ngstation having apparatus thereat `for producing from saidreceived synchronizing pulses other pulses which occur once eachsynchronizing period, said apparatus including a multi-electrodeamplifier tube and means for supplying to said amplifier tube pulsesrepresentative of the reved intelligence carrying channel pulses and theVsynchronizing pulses, a circuit coupled to the output of said amplifierfor producing voltages of one amplitude in response to the channelpnlses'and voltages of a higher amplitude in response to thesynchronizing pulses, an, electron discharge' device coupledto theoutput ci said last circuit and normally biased tobe nonconductive.:said tube being responsive only to (voltages of saidhigher amplitude inorder to pass current, a self-restoring electronic trigger circuitcoupled to and responsive to the flow of current in said electrondischarge device for producing a pulse, and a feed-back circuit fromsaid trigger circuit to an electrode of said amplifer for feeding backto said amplifier a pulse which prevents the now of current in saidampliiier, the time constants ci said trigger circuit being such that itsupplies said feed-back circuit with a pulse whose duration extends overthe major portion of the synchronizing period.

4. In a time division multiplex system for receiving periodicallyrecurring controlling or synchronizing pulses between which arepositioned intelligence carrying pulses, apparatus Ifor conver-ting saidsynchronizing pulses to other pulses which occur once each synchronizingperiod, said apparatus including a multi-electrode vacuum tube and meansfor supplying to said tube pulses representative or" the receivedintelligence carrying pulses and the synchronizing pulses, a triangularwaveform generator coupled to the output of said tube for producingtriangular-shaped `voltage waves oi one amplitude in response to theintelligence carrying pulses and triangularshaped voltage waves of ahigher amplitude in response to the synchronizing pulses, a pulsegenerator circuit responsive solely to the voltage waves of said higheramplitude for producing substantially flat-top pulses, and a feed-backcircuit from said pulse generator circuit to an electrode oi said tubefor feeding back to said tube a pulse which prevents the flow of currentin said tube, the time constants of said pulse generator being such thatit supplies said feedback circuit with a pulse whose duration extendsover the major portion of the synchronizing period.

5. In a time division multiplex system for receiving periodicallyrecurring synchronizing pulses between which are positioned intelligencecarrying pulses, apparatus for converting said synchronizing pulses toother pulses which occur once each synchronizing period, said apparatusincluding a multi-electrode vacuum tube and means for supplying to saidtube pulses representative of the received intelligence carrying pulsesand the synchronizing pulses, a triangular waveform generator coupled tothe output of said tube for producing triangular-shaped voltage waves ofone amplitude in response to the intelligence carrying pulses andtriangular-shaped voltage `'waves of a higher amplitude in response tothe synchronizing pulses, a pulse generator, and elecltronic meansresponsive to each wave of higher amplitude produced by said triangularwaveform generator for tripping said pulse generator, and a feed-backcoupling, the output of said pulse generator to an electrode of saidtube, the pulses produced by said pulse generator having such durationas to extend over the major portion of the synchronizing period.

6. In a pulse selective system, a multi-electrode amplier tube, meansfor supplying to the input ci said tube recurring trains of pulses ineach train of which at least one pulse is of different character thanthe others in that train, a diode having its cathode coupled to theoutput of said amplifier tube, a condenser connected between the anodeof said diode and ground, a resistor in shunt to said condenser, anormally conducting triode having its grid connected to the anode ofsaid diode and its cathode connected to ground, a resistor connectingthe anode of said triode to the positive terminal of a source ofunidirectional potential, a condenser connected between the anode ofsaid triode and ground, said triode and last condenser forming asawtooth generator, another triode normally biased to the anode currentcut-01T condition, a resistor connecting the anode of said last triodeto said positive terminal, a connection from the grid of said lasttriode to the anode of said rst triode, a pulse generator coupled to theanode of said last triode, and a feed-back circuit from the output ofsaid pulse generator to an electrode of said amplifler for supplyingsaid amplifier with pulses of such magnitude and polarity as to cut oithe flow of current in said amplier, the duration of the pulse producedby said pulse generator extending over the major part of the timeoccupied by said train of pulses.

7. In a time division pulse multiplex receiving system, an amplifiertube, means for supplying to the input of said tube recurring trains ofpulses in each train of which there are a plurality of intelligencecarrying pulses and a synchronizing pulse of different character thansaid intelligence carrying pulses, a triangular waveform generator meanscoupled to the output of said amplifier, means for causing saidtriangular waveform generator to produce a triangular-shaped voltagewave of higher amplitude for each said synchronizing pulse in the trainthan for the intelligence carrying pulses in the train, an electroniccircuit responsive solely to the triangular voltage wave of higheramplitude for producing a substantially flat-top wave pulse, and afeed-back circuit from said electronic circuit to said amplifier tube,the pulse in said feed-back circuit having such magnitude, polarity andduration as to prevent the flow of anode current in said amplifier tubefor the major part of the period occupied by a train of pulses.

8. In a time division pulse multiplex communication system wherein aplurality of intelligence carrying channel pulses and one or moresynchronizing pulses are transmitted each synchronizing period and arerepeated, a receiving station having apparatus thereat for producingfrom said received synchronizing pulses other pulses which occur onceeach synchronizing period, said apparatus including a multi-electrodeamplifier tube having a screen grid and means for supplying to said tubepulses representative of the received intelligence carrying channelpulses and the synchronizing pulses, a circuit coupled to the output ofsaid ampliiier for producing voltages of one amplitude in response tothe channel pulses and voltages of a higher amplitude in response to thesynchronizing pulses, a pulse generator responsive to pulses solely ofsaid higher amplitude for producing correspondingly positioned pulses,and a feed-back circuit coupling the output of said pulse generator tothe screen grid electrode of said amplifier tube, each pulse produced bysaid pulse generator being of negative polarity and of such duration asto prevent the flow of current in said amplifier tube for the majorportion of the succeeding synchronizing period.

9. In a pulse multiplex communication system wherein a plurality ofchannel pulses and one or more synchronizing pulses are transmitted eachsynchronizing period and are repeated, a receiving station havingapparatus thereat for producing from said received synchronizing pulsesother pulses which occur once each synchronizing period, said apparatusincluding a multi-electrode amplifier tube to which are applied pulsesrepresentative of the received pulses, said amplier tube including acathode, a circuit coupled to the output of said amplifier for producingvoltages of one amplitude in response to the channel pulses and voltagesof a higher amplitude in response to the synchronizing pulses, a pulsegenerator responsive to pulses solely of said higher amplitude, and afeed-back circuit coupling the output of said pulse generator to anelectrode of said amplifier, said feed-back circuit including a triodeWhose cathode is connected to the cathode of said amplifier forsupplying to said amplifier a pulse of positive polarity and of suchmagnitude and duration as to prevent the ilow of current in saidamplifier for the major portion of the succeeding synchronizing period.

WILLIAM D. HOUGHTON.

REFERENCES CITED The following references are of record in the le ofthis patent:

UNITED STATES PATENTS Number Name Date 2,113,011 White Apr. 5, 19382,141,343 Campbell Dec. 27, 1938 2,199,634 Koch May 7, 1940 2,300,999Williams Nov. 3, 1942 2,359,447 Seeley Oct. 3, 1944 2,399,135 Miller eta1 Apr. 23, 1946 2,406,019 Labln Aug. 20, 1946 2,416,305 Grieg Feb. 25,1947

